1. Field of the Invention
The present invention relates to a transistor-type pressure sensor structure. More particularly, the present invention relates to a transistor-type pressure sensor structure having a soft and flexible electrode with a stepped surface profile, and a fabrication method thereof.
2. Description of Related Art
Pressure measurements, such as atmospheric pressure or hydraulic pressure measurement, are an important part for industrial control. Generally, principles and methods of the pressure measurement are diversified, and different design methods can be applied to different fields or requirements. The current design methods for a pressure sensor include resistor type, voltage type, capacitor type, potentiometer type, inductance bridge type, strain gauge type and semiconductor pressure sensor etc.
Due to great reduction of sizes of the pressure sensors, and restrictions of fabrication processes, assembling and operations thereof, a new micro-processing technology referred to as a micro electro-mechanical system (MEMS) is developed. The MEMS has advantages of miniaturization, batch production, etc, and therefore it has been applied to other types of the pressure sensors. However, as to most of the conventional pressure sensor structures, an additional transistor is still required for receiving an output signal of the pressure sensor.
In the conventional pressure sensors, U.S. Pat. No. 6,880,406 discloses a semiconductor pressure sensor, in which a capacitor-type pressure sensor is fabricated based on a MEMS fabrication process to coordination with a control circuit (such as a complementary metal-oxide-semiconductor (CMOS) control circuit) for receiving and processing an output signal of a plate capacitor. However, according to this patent, a pressure-sensing function is not directly integrated with a field effect transistor.
Moreover, U.S Application no. 20060205013 discloses a biosensor using the field effect transistor, in which a ligand is combined to a surface of the gate of the field effect transistor, and the ligand can be connected to an end of a nucleic acid for increasing a Debye length. The ligand is selectively combined to a side of the nucleic acid for attaching the nucleic acid on the gate surface. Under such circumstances, the nucleic acid is parallelly attached to the gate surface, and is not perpendicular to the gate surface, so as to generate an effective depletion region.